The present invention relates to a piston for an engine.
Conventionally, a piston that has a resin coating film and recessed parts on a surface of a skirt part for the purpose of reducing piston slap noise and reducing friction of the skirt part is known as a piston for an engine.
However, according to this conventional art, in which the plurality of recessed parts are discretely disposed in spots in the single continuous resin coating film, the function of reducing friction of the skirt part is insufficient because it is difficult to supply oil to the recessed parts.
An object of the present invention is to improve supply of engine oil to a recessed part of a piston for an engine which has a resin coating film and recessed parts on a surface of a skirt part.
The present invention concerns a piston for an engine, the piston including a resin coating film and a recessed part on a surface of a skirt part, wherein resin coating films are distributed in a patchy fashion on the surface of the skirt part, and the recessed part, which is formed by the surface of the skirt part between adjacent ones of the patchy resin coating films and by the adjacent resin coating films, constitutes a net-like groove, and wherein outer-edge resin coating films extending in a piston movement direction are provided at ends, in a piston circumferential direction, of the skirt part.
According to the present invention, an engine oil holding region can be formed throughout a wide range of the skirt part. Since the resin coating films are distributed in a patchy fashion and the recessed part formed between the patchy resin coating films constitutes the net-like groove on the surface of the skirt part, an engine oil holding region can be formed throughout a wide range of the skirt part.
Since the surface of the skirt part are textured so as to be divided into a plurality of parts, an engine oil passage in the piston movement direction can be provided. This makes it possible to more effectively supply engine oil to each portion. Since the net-like groove is formed by the recessed part, oil can be actively supplied to the recessed part by using reciprocating movement of the piston.
Since both ends, in the piston circumferential direction, of the net-like groove formed by coating of the resin coating films on the skirt part are closed or narrowed by the outer-edge resin coating film, it is harder for engine oil introduced into the skirt part to escape in the piston circumferential direction, and it is therefore easier to hold oil in the skirt part (mainly in the net-like groove).
Since oil can be efficiently held in the skirt part, positive pressure is generated in a fluid membrane produced by oil. This floats sliding surfaces, thereby reducing friction. It is therefore anticipated that fuel consumption is reduced. Furthermore, seizure resistance of the engine improves. In particular, oil can be held even in the cold.
As a result, it is possible to provide a piston for an engine that makes it possible to improve supply of engine oil to a recessed part of a piston coated with a resin coating film.
Embodiments of a piston according to the present invention is described below with reference to the drawings. The following discusses a piston for a vertical-type diesel engine as the piston according to the present invention. In the drawings, for simplification of illustration, a resin coating film 2 of a skirt part 1 that is a cylindrical surface is illustrated in an unfolded state. Hereinafter, engine oil that is lubricating oil is simply referred to as oil.
As illustrated in
An air intake valve 18, an air release valve 19, and a fuel injector 20 are attached to the cylinder head 15.
As illustrated in
As illustrated in
The skirt part 1 of the piston 12 has, on a surface 1a thereof, a resin coating film 2 and a recessed part 3 formed by the resin coating film 2. A main body of the piston 12 is made of a metal such as cast iron or an aluminum alloy. The resin coating film 2 is made of a resin such as a polyamide resin, an epoxy resin, a phenolic resin, a silicone resin, or a polyimide resin. The resin coating film 2 contains an inorganic solid lubricant such as a transition metal oxide or graphite.
Next, for example, the resin coating film 2 and the recessed part 3 provided on the skirt part 1 and a coating pattern of the resin coating film 2 are described.
As illustrated in
The patchy resin coating films 2a and the recessed part 3 that are provided on the skirt part 1 are located on the thrust side 12a and the anti-thrust side 12b of the piston 12. The thrust side 12a is a side on which the piston 12 is pressed against the cylinder 14 by explosive pressure when the piston 12 moves downward due to rotation direction of the crankshaft 17 and inclination of the connecting rod 16 in an explosion step, and the anti-thrust side 12b is a side opposite to the thrust side 12a.
As illustrated in
Accordingly, adjacent patchy resin coating films 2a and 2a overlap each other in the piston movement direction 6 and the piston circumferential direction 8. In the example of
A plurality of patchy resin coating films 2a are disposed at predetermined intervals in the piston circumferential direction 8 of the skirt part 1 so as to constitute a resin coating film row 5, and a plurality of resin coating film rows 5 are aligned in the piston movement direction 6 so as to be shifted by a half pitch from one another in the piston circumferential direction. As a result, the patchy resin coating films 2a are disposed in a plurality of rows in a staggered pattern.
Each of openings 7a and 7b at both ends, in the piston movement direction 6, of a groove part 7 (=the recessed part 3) formed between adjacent patchy resin coating films 2a and 2a of each resin coating film row 5 faces a patchy resin coating film 2a of a resin coating film row 5 that is adjacent in the piston movement direction 6, more specifically, faces a center, in the piston circumferential direction 8, of the patchy resin coating film 2a.
As illustrated in
A vertical length L that is a length, in the piston movement direction 6, of the outer-edge resin coating film 2b is set to such a degree as to stretch over the entire length, in the piston movement direction, of an end, in the piston circumferential direction, of the skirt part 1. More specifically, the vertical length L stretches over the five resin coating film rows 5 that are aligned in the piston movement direction 6 and is slightly shorter than an entire length D (see
In the piston 12 according to the first embodiment, an oil holding region can be formed throughout a wide range of the skirt part 1. Since a large number of resin coating films 2a are distributed in a patchy fashion and the recessed part 3 that is formed between the patchy resin coating films 2a forms the net-like groove 4 on the surface 1a of the skirt part 1, the oil holding region can be formed throughout a wide range of the skirt part 1.
The recessed part 3 that is formed between patchy resin coating films 2a that are adjacent in the piston circumferential direction 8 of the skirt part 1 is adjacent to other patchy resin coating films 2a in the piston movement direction 6. This allows oil flowing out from the openings at both ends of the recessed part 3 due to reciprocating movement of the piston 12 to collide with patchy resin coating films 2a that are adjacent in the piston movement direction 6, thereby reducing flow of engine oil out of the recessed part 3. It is therefore possible to increase the oil holding function of the net-like groove 4.
Since the surface 1a of the skirt part 1 is textured so as to be divided into plural parts, a passage for oil in a top-bottom direction (the piston movement direction 6) can be provided. This allows oil to be more effectively supplied to each portion. Since the resin coating film rows 5 and 5 that are adjacent in the piston movement direction 6 are shifted from one another in the piston circumferential direction 8 so that the patchy resin coating films 2a are arranged in a staggered pattern, oil can be actively supplied to the recessed part 3 by using reciprocating movement of the piston 12.
Since both ends, in the piston circumferential direction 8, of the net-like groove 4 that is formed by coating of the resin coating films 2, 2a, and 2b on the skirt part 1 are closed by the outer-edge resin coating film 2b, it is harder for oil introduced into the skirt part 1 to escape in the piston circumferential direction. That is, oil is more likely to be held in the skirt part 1 (mainly in the net-like groove 4). The resin coating film 2 can be made in contact with a cylinder liner in a portion having large rigidity at both ends, in the piston circumferential direction 8, of the skirt part 1.
Since oil can be efficiently held in the skirt part 1, positive pressure is generated in a fluid membrane produced by oil. This floats sliding surfaces, thereby reducing friction. It is therefore anticipated that fuel consumption can be reduced. Furthermore, seizure resistance of the engine improves. In particular, oil can be held even in the cold.
The piston 12 may be coated with the resin coating film 2 in a pattern illustrated in
Accordingly, each of openings 7a and 7b at both ends, in the piston movement direction 6, of a groove part 7 (=the recessed part 3) formed between adjacent patchy resin coating films 2a and 2a of each resin coating film row 5 faces a patchy resin coating film 2a of a resin coating film row 5 that is adjacent in the piston movement direction 6, more specifically, a center, in the piston circumferential direction 8, of the patchy resin coating film 2a, as illustrated in
In the piston 12 according to the second embodiment, an included angle θ formed between left and right end surfaces 11 and 11 of a V-shaped end, in the piston movement direction 6, of each patchy resin coating film 2a is set to 120 degrees (or 120 degrees±20 degrees). Although an effect can be produced by setting θ to a range of 60 degrees≦θ<180 degrees, the range “120 degrees±20 degrees” is preferable to achieve a better effect.
In the piston 12 according to the second embodiment, lubricating oil moving in the recessed part 3, i.e., the groove part 7 between patchy resin coating films 2a and 2a adjacent in the piston circumferential direction 8 flows out of the opening 7a, collides with and is received by an end of a patchy resin coating film 2a adjacent in the piston movement direction 6, and is bounced back by the pair of end surfaces 11 and 11 in accordance with movement (rising and falling movement) of the piston 12.
A saw-tooth-like recessed part that is formed by ends of adjacent patchy resin coating films 2a and extends in the piston circumferential direction 8 is configured to serve as an oil accumulating groove that is excellent in lubricating oil holding function.
As illustrated in
Also in this case, the outer-edge resin coating film 2b is a vertically long part that connects endmost patchy resin coating films 2a, in the piston circumferential direction 8, of a plurality of (10) resin coating film rows 5 aligned in the piston movement direction 6 and has projections 28 facing inward in the piston circumferential direction 8 so as to encompass the patchy resin coating films 2a.
As illustrated in
Furthermore, it is also possible to employ a piston 12 in which an extended band part 9a extending upward from a band-like part 9 of an outer-edge resin coating film 2b is provided so that both sides, in the piston circumferential direction 8, of the band-like bear part 21 is blocked in the piston circumferential direction 8, as illustrated in
Since the band-like bear part 21 having no resin coating film 2 is provided at the upper end of the skirt part 1, it is easier to introduce oil from the band-like bear part 21 into a portion of the resin coating film 2, for example, a net-like groove 4. In cases where the band-like bear part 21 having the extended band part 9a that is a wall of the resin coating film 2 is provided in the piston circumferential direction 8 as illustrated in
It is also possible to employ a piston 12 in which outer-edge resin coating films 2b at respective ends, in a piston circumferential direction 8, of the skirt part 1 are shaped so that central parts thereof in the piston movement direction 6 bulge in the piston circumferential direction 8, more specifically, bulge inward (toward each other), as illustrated in
In the piston 12 having the bulging outer-edge resin coating films 2b, oil can be guided by upper and lower inclined sides 22 and 22 to a central part, in the piston circumferential direction 8, of the skirt part 1, i.e., to a part that strongly makes contact with the cylinder 14 (see
It is also possible to employ a piston 12 in which a recessed pocket part 23 that is a recess of the surface 1a of the skirt part 1 is provided at an end, in the piston movement direction 6, of the skirt part 1, as illustrated in
Since oil can be accumulated in the recessed pocket part 23, the recessed pocket part 23 can function as an oil pocket of the skirt part 1. Since the inclination angles of the recessed pocket part 23 are set to α>β, oil is more easily accumulated in the recessed pocket part 23 when the piston 12 moves upward, and the accumulated oil can be supplied to the skirt part 1 when the piston 12 moves downward. In cases where the recessed pocket part 23 is provided at an upper end of the skirt part 1 (not illustrated), it is desirable that the angles be set in an opposite manner to those described above, specifically set to α<β.
It is also possible to employ a piston 12 in which patchy resin coating films 2a provided on the surface 1a of the skirt part 1 in a direction that crosses a direction of an axis P of a piston pin (not illustrated) may be provided on a surface of the piston 12 that has been subjected to shot-peening treatment, i.e., a rough surface 24, as illustrated in
The patchy resin coating films 2a coating the rough surface 24 that has been subjected to shot-peening treatment is less likely to peel off than patchy resin coating films 2a coating the normal surface 1a and therefore can contribute to an improvement of wear resistance.
It is also possible to employ a piston 12 in which a groove 25 extending in the piston movement direction 6 is provided at ends of the respective circumferentially end parts 1A of the skirt part 1 that are close to the circumferentially central part 1B, as illustrated in
In the piston 12 according to the seventh embodiment, oil can be actively supplied to a portion of the resin coating film 2 through the grooves 25 in accordance with rising and falling movement of the piston 12. It is therefore less likely that shortage of an oil membrane occurs. This can contribute to an improvement of fuel consumption and prevention of noise.
It is also possible to employ a piston 12 in which a circumferential resin coating film 2c extending in the piston circumferential direction 8 is provided at an end, closer to the crankshaft 17 (see
The circumferential resin coating film 2c provided at the lower end of the skirt part 1 is shaped along lower edges of the respective circumferentially end parts 1A and a lower edge of the circumferentially central part 1B, as illustrated in
The circumferential resin coating film 2c illustrated in
It is also possible to employ a piston 12 in which the oil hole 27 provided in a lowermost circumferential groove 26 is elongated downward, as illustrated in
It is anticipated that the oil hole 27 that is elongated downward makes it easy to supply oil from the oil hole 27 to a portion of the resin coating film 2. Furthermore, since a wall surface of the oil hole 27 on the resin coating film 2 side is the inclined surface 27a that is curved inward, supply of oil from the oil hole 27 to a portion of the resin coating film 2 is promoted.
A piston for an engine according to the present invention has following features (1) through (6).
(1) Lengths, in the piston movement direction 6, of the outer-edge resin coating films 2b are set to such a degree as to stretch over an entire length, in the piston movement direction 6, of ends, in the piston circumferential direction 8, of the skirt part 1.
Accordingly, since the length, in the piston movement direction, of the outer-edge resin coating film is set to such a degree as to stretch over the entire length, in the piston movement direction, of an end, in the piston circumferential direction, of the skirt part, it is harder for engine oil introduced into the skirt part to escape in the piston circumferential direction. This increases the effect of holding engine oil in the skirt part.
(2) The outer-edge resin coating films 2b are shaped so that central parts thereof in the piston movement direction 6 bulge in the piston circumferential direction 8.
Accordingly, since the central part, in the piston movement direction, of the outer-edge resin coating film bulges in the piston circumferential direction, engine oil is guided by inclined sides of the bulged part so as to be collected toward a central part, in the piston circumferential direction, of the skirt part in accordance with sliding movement of the piston. Accordingly, engine oil in the skirt part can be guided to a part of the skirt part that strongly makes contact with a cylinder in accordance with movement of the piston. This can contribute to an improvement of lubricating performance.
(3) The patchy resin coating films 2a have a hexagonal shape and/or an hourglass shape.
Accordingly, in cases where each of the patchy resin coating films has a hexagonal shape, engine oil is supplied to the net-like groove well due to upward and downward movement of the piston, and as a result smooth lubrication effect is obtained.
In cases where each of the patchy resin coating films has an hourglass shape, lubricating oil moving in the recessed part between patchy resin coating films that are adjacent to each other in the piston circumferential direction in accordance with movement of the piston flows out from an opening of the recessed part, and collides with and is received or bounced back by an end of a patchy resin coating film that is adjacent in the piston movement direction. This can provide an excellent engine oil holding function.
(4) A recessed pocket part 23 that is a recess of the surface 1a of the skirt part 1 is provided at an end, in the piston movement direction 6, of the skirt part 1.
Accordingly, oil can be accumulated in the recessed pocket part that is a recess in the surface of the skirt part at an end, in the piston movement direction, of the skirt part. The recessed pocket part can function as an oil pocket of the skirt part and therefore can contribute to a further improvement of lubricating performance.
(5) In a part of the surface 1a of the skirt part 1 in a direction that crosses a direction of an axis P of a piston pin, the patchy resin coating films 2a are provided on a rough surface 24 of the piston 12 that has been subjected to shot-peening treatment.
Accordingly, since the patchy resin coating films in a part of the surface of the skirt part in a direction that crosses an axial direction of a piston pin are provided on a surface that has been subjected to shot-peening treatment, these patchy resin coating films are less likely to peel off than patchy resin coating films coating a normal surface and therefore can contribute to an improvement of wear resistance.
(6) A circumferential resin coating film 2c that extends in the piston circumferential direction 8 is provided at an end, farther from a crankshaft, of the skirt part 1 on a thrust side 12a and/or an end, closer to the crankshaft, of the skirt part 1 on an anti-thrust side 12b.
Accordingly, the circumferential resin coating film functions as a continuous wall that covers, in the piston circumferential direction, an end, in the piston movement direction, of the net-like groove of the skirt part. This makes it harder for oil taken into the net-like groove to escape in the piston movement direction. This can contribute to an improvement of wear resistance. In this case, preferably, the circumferential resin coating film is provided at an end of the skirt part farther from the crankshaft on the thrust side, and the circumferential resin coating film is provided at an end of the skirt part closer to the crankshaft on the anti-thrust side since engine oil is more likely to be held in a portion that is strongly pressed against the cylinder.
Number | Date | Country | Kind |
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2016-109746 | Jun 2016 | JP | national |